If you need to measure length, width, area in the usual way, then this laser rangefinder will be a good purchase. And if you want to measure, determine by the Pythagorean theorem, also measure depth and angle, then you should think about purchasing. (Although errors in determining heights can only be in my device) As for the discrepancy of -3 mm, this is fixable. Calibration in this device is carried out from -7 to +7 mm. I found the discrepancy in a test with a laser rangefinder from another manufacturer and a classic metal tape measure of not cheap quality. Photo below. I hope I helped you with your choice.